Cyanate ester resins, developed during the 1980s, join epoxy resins and bismaleimide resins as the third major class of thermosetting resins. Polycyanurates or cross-linked cyanate resins are prepared by the cyclopolymerization of aromatic cyanate esters. These cyanate esters are bisphenol derivatives containing a plurality of cyanate functional groups. When heated, the cyanate functionality undergoes exothermic trimerization to form substituted triazine rings. Subsequent curing produces the thermosetting resin.
Cyanate esters are currently employed in rapidly curing adhesive compositions used to bond semiconductor devices or chips, also known as dice, to carrier substrates. Such adhesive compositions include, in addition to the cyanate ester, thermally and/or electrically conductive filler and a curing catalyst. These adhesive compositions have eliminated many of the deficiencies inherent in epoxy adhesives and polyimide adhesives such as low glass transition temperature, high degree of ionic contamination, retention of solvent and lengthy cure. However, cyanate ester containing attach paste compositions presently available exhibit some deficiency with respect to homogeneity, i.e. such pastes have a tendency to become non-homogeneous at ambient temperature.